Al Jazeera's Hoda Abdel Hamid, reporting from Istanbul, said it would have been impossible for the US to agree to Erdogan's demands that all PKK bases be shut down and the group's leaders handed over to Ankara.

"The US has very limited resources at this stage in Iraq, and it certainly doesn't have the resources to pull out from the other troubled areas and put them in the northern mountains," she said.

Ankara has come under increased public pressure to act against the PKK after about 40 Turks, mostly troops, were killed in a series of attacks.

The White House has expressed concern that a cross-border incursion by the Turkish military could destabilise to what has been the calmest part of Iraq.

Kurdish protests

As the two leaders met, hundreds of ethnic Kurds gathered outside the White House chanting "stop the Turkish invasion".